Examination of the 2 /sup 1/A/sub 1/ states of formaldehyde and ketene including analytic configuration interaction energy first derivatives for singlet excited electronic states of the same symmetry as the ground state
In an accompanying paper by Lee, Allen, and Schaefer (J. Chem. Phys. 87, xxxx (1987)), an efficient formulation for the analytic evaluation of two-configuration self-consistent-field configuration interaction (TCSCF-CI) energy first derivatives is presented. In this paper the TCSCF-CI gradient method is adapted and applied to singlet excited electronic states of the same symmetry as the ground state. Since single-configuration self-consistent-field configuration interaction (SCF-CI) wave functions are unreliable for such electronic states due to the possibility of variational collapse, the TCSCF-CI method based on excited-state orbitals is the simplest means by which dynamical electron correlation can be incorporated effectively. Geometrical structures, excitation energies, and harmonic vibrational frequencies obtained with double-zeta plus polarization (DZP) and DZP+Rydberg (DZP+R) basis sets are reported for the 2 /sup 1/A/sub 1/ states of formaldehyde and ketene. The 2 /sup 1/A/sub 1/ state of H/sub 2/CO is found to have two distinct minima with C/sub 2//sub v/ symmetry: a (..pi --> pi..*)/sup 1/ valence minimum with r/sub e/(C--O) = 1.564 A and T/sub 0/ = 8.50 eV, and an (n..-->..3p/sub y/)/sup 1/ Rydberg minimum with r/sub e/(C--O) = 1.216 A and T/sub 0/ = 7.93 eV. Some question exists on whether the (n..-->..3p/sub y/)/sup 1/ state occurs experimentally at 8.11 or 7.96 eV, but in either case the agreement between theory and experiment is good.
- Research Organization:
- Department of Chemistry and Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 5964077
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 87:12
- Country of Publication:
- United States
- Language:
- English
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